Some Elements of an Operating System

Lecture P2: Interacting with the OS

Files. ■

Abstraction for storage (disks, DVD).

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File manipulation commands.

Processes. ■

Abstraction for processor (CPU).

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Launching an application = initiating a process.

Interactions. ■

Between user and machine.

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Among network of machines.

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Between files and processes.

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I/O redirection and pipes.

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User Interface

Files

Point and click. ■

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/

File.

User launches applications by clicking. – Compile → Project → hello.c

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Restricted to pre-packaged menu options. ■

Sequence of bits.

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aaclarke

User types commands at terminal. % gcc hello.c

lib

etc

u

Extended for things beyond disks.

Command line. ■

bin

A simple and powerful abstraction for permanent storage (disks).

cs126

zrnye

Directory. ■

Easily customizable. % gcc126 hello.c

Sequence of files (and other directories). files

submit

Filename.

Extends to complex command sequences.

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Sequence of directory names on the path stock from "/" to the file.

mandel

See "In the Beginning was the Command Line" by Neal Stephenson. ■

http://www.spack.org/words/commandline.html

Implements folder abstraction.

mand32.txt

/u/cs126/files/mandel/mand32.txt C:\cs126\files\mandel\mand32.txt 3

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Processes

Process Interconnection Abstractions

Process.

Standard input, standard output.

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An abstraction for the processor (CPU).

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Launching an application = initiating a process.

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Abstract files for command interfaces.

Redirection: Multitasking. ■

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Illusion of multiple machines for your use. – abstraction provided by operating system – outgrowth of 1960s "time-sharing"

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Use it by opening one window for each application. – browser, editor, terminal window

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random > saveanswer

Standard output to file. – File → Save As Standard input from file. – File → Open – drag-and-drop Standard input from file, standard output to file.

3

average < saveanswer

sort < myfile > myfilesorted

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Piping: ■

Connect standard output of one command to standard input of the next. – not easily expressed with point-andclick interface

random | average

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I/O Redirection and Pipes

Triangle Game Game played on equilateral triangle, with vertices R, G, B. ■

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Start at R. Repeat the following: – pick a random vertex – move halfway between current point and vertex – draw a "dot" in color of vertex

B

2 5 1

What picture emerges?

3 6 4

0

R

7

G

8

Triangle Game: Boring Text Output

Turtle Graphics

triangle.c ANSI C does not directly support graphical output. #include #define N 50000 #define SQRT3 1.732050808 int randomInteger(int n) { ... }

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int main(void) { int i, r; double x = 0.0, y = 0.0, x0, y0;

Need help from OS. In this course we use "turtle graphics language." – render with PostScript, OpenGL, or Java

Turtle graphics. ■

for (i = 0; i < N; i++) { r = randomInteger(3); if (r == 0) { x0 = 0.0; y0 = 0.0; } else if (r == 1) { x0 = 512.0; y0 = 0.0; } else if (r == 2) { x0 = 256.0; y0 = 256 * SQRT3; } x = (x0 + x) / 2.0; y = (y0 + y) / 2.0; printf("%f %f\n", x, y); } return 0; }

You command turtle to move, turn, and draw using relative coordinates.

D R D R D R

512 120 512 120 512 120

(512, 0) 10

triangle.c #include #include #define N 50000 #define SQRT3 1.732050808 int randomInteger(int n) { ... }

You also command turtle to fly to absolute coordinates and and drop colored spots below.

int main(void) { int i, r; double x = 0.0, y = 0.0, x0, y0; printf("F 0 0\n"); printf("D 512 R 120 D 512 R 120 D 512 R 120\n");

Turtle Graphics Commands 200 60 400 1 0 80 200 100 90 50 0 0 90 100

(0, 0)

Triangle Game: Turtle Graphics Output

Flying turtle graphics.

F S F C S F D R D C R D

// Walk 512 units, pen down // Turn 120° counterclockwise

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Flying Turtle Graphics ■

(256, 256 √3)

Turtle Graphics Commands (relative)

100 100 0 400

// // // // // // // //

Fly to (200, 100) Leave spot of size 60 Fly to (400, 100) Change pen color to red Leave spot of size 80 Fly to (200, 400) Walk 100 units, pen down Fly to (400, 100)

(300, 450)

for (i = 0; i < N; i++) { r = randomInteger(3); if (r == 0) { x0 = 0.0; y0 = 0.0; } else if (r == 1) { x0 = 512.0; y0 = 0.0; } else if (r == 2) { x0 = 256.0; y0 = 256 * SQRT3; } x = (x0 + x) / 2.0; y = (y0 + y) / 2.0;

y (200, 400)

printf("F %f %f\n", x, y); printf("S 5\n");

1 (0, 0)

draw triangle

draw dot

} return 0;

x

} 11

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Triangle Game: Turtle Graphics Output Text output still boring!

Triangle Game Game played on equilateral triangle, with vertices R, G, B.

Command Line % F D D D F S F S F S F S F S

echo 5 1.5 0 0 512 R 120 512 R 120 512 R 120 128.000000 1.500000 320.000000 1.500000 160.000000 1.500000 336.000000 1.500000 424.000000 1.500000

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| triangle

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110.851252 55.425626

Start at R. Repeat the following: – pick a random vertex – move halfway between current point and vertex – draw a "dot" in color of vertex

B

2 5

27.712813 1

13.856406

What picture emerges?

6.928203

3 6 4

Write C program turtle.c to translate text into PostScript; render PostScript with ghostscript. ■

Three pipes.

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See Assignment 2.

0

R

G

Command Line % echo 5 1.5 | triangle | turtle | gs 13

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Turtle Graphics in PostScript

Turtle Graphics in PostScript

turtle.c (includes and helper functions)

turtle.c (main skeleton)

#include #include #define PI 3.1415926535897932385 // PostScript header void header(void) { printf("%%!PS-Adobe-3.0 EPSF-3.0\n"); printf("%%%%BoundingBox: 0 0 512 512\n"); } // PostScript footer void footer(void) { printf("showpage\n"); }

int main(void) { char command; double d; double a; double r, g, b; I’m a PostScript program.

double x = 0.0; double y = 0.0; double alpha = 0.0;

// // // //

input turtle command distance change in angle new RGB colors

// x coordinate of turtle // y coordinate of turtle // turtle orientation

header(); Print me out. // READ IN TURTLE GRAPHICS COMMANDS AND PROCESS footer(); return 0; } 17

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Turtle Graphics in PostScript

Turtle Graphics: Relative Coordinates Relative coordinates.

turtle.c (absolute coordinates)

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// read in turtle graphics commands and process while (scanf(" %c", &command) != EOF) { switch(command) {

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// change color to r, g, b case ’C’: scanf("%lf %lf %lf", &r, &g, &b); printf("%f %f %f setrgbcolor\n", r, g, b); break;

Current location = (x, y). Current direction = α. Turtle moves d units. New location = (x’, y’). ! x’ = x + d cos α. ! y’ = y + d sin α.

(x’, y’)

// fly to location (x, y) case ’F’: scanf("%lf %lf", &x, &y); break;

d

// draw spot of size d case ’S’: scanf("%lf", &d); printf("%f %f %f %f rectfill\n", x – d/2, y – d/2, d, d); break;

α (x, y)

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Turtle Graphics in PostScript turtle.c (relative coordinates) // rotate case ’R’: scanf("%lf", &a); alpha += a; break; // move d units in current direction, pen down case ’D’: scanf("%lf", &d); printf("%f %f moveto\n", x, y); x += d * cos((PI/180.0) * alpha); y += d * sin((PI/180.0) * alpha); printf("%f %f lineto\n", x, y); printf("stroke\n"); break; } }

// end switch // end while

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